1. Field of the invention
The present invention relates to an apparatus and method based on fiber optic interferometry, and in particular, to a tip tray apparatus for packaging of optical sensors used in detecting analytes and mechanisms for creating flow of solution.
2. Description of the Related Art
Diagnostic tests based on a binding event between members of an analyte-anti-analyte binding pair are widely used in medical, veterinary, agricultural and research applications. Typically, such methods are employed to detect the presence or amount of an analyte in a sample, and/or the rate of binding of the analyte to the anti-analyte. Typical analyte-anti-analyte pairs include complementary strands of nucleic acids, antigen-antibody pairs, and receptor-receptor binding agent, where the analyte can be either member of the pair, and the anti-analyte molecule, the opposite member.
Diagnostics methods of this type often employ a solid surface having immobilized anti-analyte molecules to which sample analyte molecules will bind specifically and with high affinity at a defined detection zone. In this type of assay, known as a solid-phase assay, the solid surface is exposed to the sample under conditions that promote analyte binding to immobilized anti-analyte molecules. The binding event can be detected directly, e.g., by a change in the mass, reflectivity, thickness, color or other characteristic indicative of a binding event. Where the analyte is pre-labeled, e.g., with a chromophore, or fluorescent or radiolabel, the binding event is detectable by the presence and/or amount of detectable label at the detection zone. Alternatively, the analyte can be labeled after it is bound at the detection zone, e.g., with a secondary, fluorescent-labeled anti-analyte antibody.
Co-owned U.S. Pat. No. 5,804,453, (the '453 patent) which is incorporated herein by reference, discloses a fiber-optic interferometer assay device designed to detect analyte binding to a fiber-optic end surface. Analyte detection is based on a change in the thickness at the end surface of the optical fiber resulting from the binding of analyte molecules to the surface, with greater amount of analyte producing a greater thickness-related change in the interference signal. The change in interference signal is due to a phase shift between light reflected from the end of the fiber and from the binding layer carried on the fiber end, as illustrated particularly in FIGS. 7a and 7b of the '453 patent. The device is simple to operate and provides a rapid assay method for analyte detection.
The optical tip tray device described herein can be used with a fiber-optic inferometer assay device, as described above. Specifically it provides a mechanism for packaging and holding discrete fiber optic sensors in a format that allows for easy use of the sensors. Before the types of assays described above are conducted, the sensors can undergo some type of pre-wetting. Techniques can also be used to immobilize molecules, such as proteins, to the surface of the sensor. “Pre-wet,” as used herein, is a procedure in which a sensor coated with immobilized binding proteins is hydrated to restore their biological activity. Sensors coated with proteins can be stored dry in order to preserve the activity of the proteins until they are to be used in an assay. In immobilization procedures, sensors are put into contact with sample solutions, such as protein-containing samples, and the proteins or other molecules in the sample are immobilized to the surface of biosensors coated with the appropriate surface chemistry. In the device disclosed herein, discrete optical sensors are packaged in a format (e.g., a format that corresponds to the 96-well format of a standard microtiter plate) that allows the sensors to be easily dipped into pre-wet or protein-immobilization solutions. Thus, in some embodiments, the device provides for off-line incubation, pre-wet, and/or immobilization. In contrast, current devices for holding biosensors are either in flow cell format or have sensors located as a part of the bottom of a microplate well, both of which require different pre-wetting and immobilization procedures. In addition, these systems do not provide flexibility for users to arrange or configure the biosensors to customize the sensor arrangement for immobilization. Users do not have the option to simply remove and save unused biosensors, but are instead forced to use an entire set of sensors for each experiment even if only a few were needed.
Therefore, there is a need for an easy mechanism for off-line incubation, pre-wetting, and immobilization where the user has the flexibility to move around the sensors and customize the arrangement. There is also a need for a device that stores these types of discrete sensors in a format for easy pick up of the sensors, for transfer of the sensors to a second microplate for assay, and for mapping of sensors to sample wells. Furthermore, these types of discrete sensors need to be packaged to avoid damage during shipping, handling, and storage of the sensors.
Current devices also have limitations with regard the mechanism for providing flow in wells during an assay. For molecular kinetic analyses and other types of analyses, the device must include some sort of mechanism for providing flow (e.g., within the wells of the microtiter plate containing sample or the second microtiter plate), for example, to measure the disassociation of molecules from the sensor surfaces. Where the sensor surface is located at the bottom of a microtiter plate, however, it is difficult to create any flow. Without proper flow, it is impossible to provide a valid environment for molecular binding kinetic analysis. Current systems use flow cells to create sample or buffer flow over the sensing surface. For example, some current systems use microfluidics and fluidic channels to move the fluid around to bring reagents into contact with a particular biosensor. However, these types of designs put a large design and support burden on the instrumentation. Thus, there is needed a mechanism that allows for fluidic motion without the need for microfluidics or fluidic channels. There is a need for a mechanism that allows exposure of the biosensor to a relatively large bulk of reagents by providing continuous flow of reagent over the biosensor.
The present invention is designed to overcome these and other limitations with a design that allows flexibility for arrangement or configuration of biosensors, biosensor mapping capability to sample wells in a microtiter plate, off-line incubation, pre-wet, and immobilization, and an effective mechanism for orbital flow of the reagent over the biosensors, among other advantages.